You just falsely assumed Paul was a Calvinist. Paul prayed as he did because He knew his prayers were effective.
Why would any Calvinist pray for God to save anyone? Why not just pray for yourself to be changed.
Paul wrote what God inspired him to write. What I believe is not from John Calvin. It is from God, written down for us by Paul and the other inspired authors of the Bible. The evidence is in scripture.
You want to take it out of the Bible and force it into John Calvin's writings. I have not read much of Calvin's writings. I have read the Bible. What I believe is also what Paul the Apostle taught.
Why would Paul pray for God to save anyone? Why not just pray for himself to be changed?
In fact, we see Paul praying that he might be changed. We see that dialogue in Romans 7 and 8. We also see Paul pray for the lost and for the elect.
Reynolds, you are asking the wrong question. It's not "why" pray... it's "For what purpose" do I pray.
The purpose is that I may be made more and more in the likeness of my King, Jesus.